The invention relates to apparatus for separating particles from a fluid flow particularly, but not exclusively, to apparatus for separating dust from an airflow in a vacuum cleaner. The invention also relates to a valve for introducing bled fluid to a mainstream fluid.
Separation apparatus incorporating at least one bleed valve is known, for example from published International patent application Ser. No. PCT/GB93/01325. In that arrangement, a bleed valve is arranged upstream of a cyclonic separator such that, if the pressure (which is normally directly related to the airflow) in the separator falls below a predetermined level, air is bled into the airflow path from the atmosphere in order to maintain a minimum airflow. This allows the cyclonic separator to operate satisfactorily and ensures that the motor is effectively cooled. Whilst this known arrangement is perfectly adequate in most cases, it has been found that there are some instances when its performance could be improved. For example, a vacuum cleaner will normally include a filter, separate from the main dust-separating apparatus, located either immediately upstream or downstream of the motor. If this filter becomes clogged, the airflow through the dust-separating apparatus (i.e. the cyclonic separator) will be reduced and this can prevent sufficient suction being developed in the dust-separating apparatus to cause the bleed valve to bleed air into the dust-separating apparatus. The result can be reduced effectiveness or efficiency of the cyclonic separator and, more importantly, an increased risk of the motor overheating.
It is also known from UK patent No. 1080504 to provide a signal device for a vacuum cleaner which operates in response to an increase in pressure differential across the bag or filter to indicate that the filter requires changing. The signal is given by bleeding air along a conduit and across a reed to give an audible indication that the filter should be changed.
It is an object of the present invention to provide a bleed valve which is not dependent upon absolute pressures in order to operate.
It is also an object of the present invention to provide improved apparatus for separating particles from a fluid flow, particularly suitable for use in a vacuum cleaner, which is capable of reliably bleeding air into the separation apparatus so as to maintain a minimum airflow therein and to reduce the risk of the motor overheating.
A further object of the invention is to provide improved apparatus for separating particles from a fluid flow, particularly suitable for use in a vacuum cleaner, which can be utilised to indicate that a blockage is present.
The invention provides a bleed valve. The invention also provides an apparatus containing a bleed valve.
The present invention further provides a valve for introducing a fluid between an inlet and outlet of an apparatus, which comprises: a valve head which is movable between an open and a closed position to open and close a first opening into the valve; a housing means having: (i) a first section, defining the first opening leading to a first chamber on one side of a flexible seal means mounted between the housing means and the valve head of the piston means to be connected by a second opening in the first section upstream of flow of the fluid in the apparatus; (ii) a second section defining a second chamber on an opposite side of the seal means and between the piston means and the second section, with a third opening in the second section to be connected downstream of a fluid flow in the apparatus; and bias means mounted so as to hold the piston means with the valve head in the open position at rest and wherein when a first flow of fluid through the apparatus includes a pressure in the second section less than the pressure in the first section, the valve head is in the closed position in the opening and the fluid is prevented from flowing through the opening in the valve and wherein when a blockage of fluid flow occurs between the inlet and the outlet of the apparatus the valve is in the open position while the fluid is flowing to admit fluid into the valve and apparatus.
The present invention also provides an apparatus having a fluid air flow between an inlet and an outlet through an element which produces a pressure drop and which is subject to becoming blocked, by means of a valve which allows fluid to be introduced between the inlet and the outlet, the improvement wherein the valve comprises a valve head which is movable between an open and a closed position to open and close a first opening into the valve in response; a housing means having: (i) a first section, defining the first opening leading to a first chamber on one side of a flexible seal means mounted between the housing means and the valve head of the piston means connected by a second opening in the first section upstream of flow of fluid in the apparatus; (ii) a second section defining a second chamber on an opposite side of the seal means and between the piston means and the second section, with a third opening in the second section connected downstream of a fluid flow in the apparatus; and bias means mounted so as to hold the piston means with the valve head in the open position at rest and wherein when a first flow of fluid through the apparatus includes a pressure in the second section less than the pressure in the first section, the valve head is in the closed position in the opening and the fluid is prevented from flowing through the opening in the valve and wherein when a blockage of fluid flow occurs between the inlet and the outlet of the apparatus, the valve is in the open position while the fluid is flowing to admit fluid into the valve and apparatus.
The provision of a bleed valve which is responsive to a drop in the pressure differential measured across the separation apparatus means that ambient fluid is bled more reliably into the flow path. This is because the pressure drop across the separation apparatus, particularly cyclonic separation apparatus, is directly related to the flow rate. The pressure losses are due primarily to friction which is highly dependent upon the flow rate. The higher the flow rate, the greater the pressure drop across the cyclonic separation apparatus.
It is important to maintain an adequate flow rate through separation apparatus, particularly cyclonic separation apparatus, if good separation is to be maintained. It is also very important to maintain an adequate flow of cooling air or other fluid past a motor in order to avoid overheating. The present invention therefore represents a significant improvement over the prior art.
Since a drop in the pressure differential (i.e. flow rate) across the separation apparatus is indicative of a blockage in the flow path, the operation of the bleed valve can also be used to indicate that a blockage is present and provide a signal to the user that maintenance is required. In the prior art arrangements, a blockage located between the separation apparatus and the fan or motor can fail to cause the bleed valve to operate.
A further advantage of the present invention is that the bleed valve will normally be open when the motor is switched off. In the prior art arrangement, the bleed valve would be shut and may not open if a blockage is present at the time the motor is switched on. In the apparatus according to the invention, the bleed valve stays open until a sufficient pressure drop is achieved across the dust-separating apparatus. This ensures that the motor is adequately cooled at all times.